It is well recognized that water handling systems used in a spacecraft are prone to failure caused by biofouling and mineral scaling, which can clog mechanical systems and degrade the performance of capillary-based technologies. Long duration spaceflight applications, such as extended stays at a Lunar Outpost or during a Mars transit mission, will increasingly benefit from hardware that is generally more robust and operationally sustainable overtime. This paper presents potential design and testing considerations for improving the reliability of water handling technologies for exploration spacecraft. Our application of interest is to devise a spacecraft wastewater management system wherein fouling can be accommodated by design attributes of the management hardware, rather than implementing some means of preventing its occurrence

Klaus, David M.

Thomas, Evan A.

English

PDXScholar (Portland State University)

Portland State UniversityPDXScholarMechanical and Materials Engineering FacultyPublications and Presentations Mechanical and Materials Engineering1-1-2009Developing Sustainable Spacecraft Water Management SystemsEvan A. ThomasPortland State UniversityDavid M. KlausUniversity of Colorado at BoulderLet us know how access to this document benefits you.Follow this and additional works at: https://pdxscholar.library.pdx.edu/mengin_facPart of the Systems Engineering CommonsThis Article is brought to you for free and open access. It has been accepted for inclusion in Mechanical and Materials Engineering Faculty Publicationsand Presentations by an authorized administrator of PDXScholar. For more information, please contact pdxscholar@pdx.edu.Citation DetailsThomas, E., Klaus, D., Developing Sustainable Spacecraft Water Management Systems, 2009-2010 Decadal Survey on Biological andPhysical Sciences in Space, National Research Council of The National Academies, 20092009-2010 Decadal Survey on Biological and Physical Sciences in SpaceNational Research Council of The National AcademiesTranslation to Space Exploration SystemsWhite Paper SubmissionDeveloping Sustainable Spacecraft Water Management SystemsEvan A. ThomasNASA- Johnson Space CenterDavid M. KlausUniversity of Colorado at BoulderAbstractIt is well recognized that water handling systems used in a spacecraft are prone to failurecaused by biofouling and mineral scaling, which can clog mechanical systems and degrade theperformance of capillary-based technologies. Long duration spaceflight applications, such asextended stays at a Lunar Outpost or during a Mars transit mission, will increasingly benefitfrom hardware that is generally more robust and operationally sustainable overtime.This paper presents potential design and testing considerations for improving the reliability ofwater handling technologies for exploration spacecraft. Our application of interest is to devise aspacecraft wastewater management system wherein fouling can be accommodated by designattributes of the management hardware, rather than implementing some means of preventingits occurrence.IntroductionDevelopment of spacecraft life support hardware over the past few decades has focusedprimarily on microgravity applications, with sophisticated designs usually constrained bylimitations of volume, mass and power. In particular, for 2-phase gas/liquid separation inmicrogravity, centripetal acceleration or capillary action is used to remove liquids without theaid of gravity-driven buoyancy. These systems have often been prone to failure due to fluidfouling caused by biological reactions or mineral scaling, which can clog mechanical systemsand degrade the performance of capillary-based systems. In turn, these failures can causeincreased maintenance cost and overall crew labor burden.Long duration space missions, such as expected for a Lunar Outpost or a Mars transit, will drivethe need for hardware that is less prone to fouling failure and generally more robust andsustainable. One application that would benefit from innovation is wastewater management,wherein wastewater fouling can be accommodated by the design of the fluid managementhardware as opposed to its occurrence being detrimental to the desired process.This paper presents challenges associated with spacecraft water system fouling and suggestsalternative approaches that move toward increased sustainability. Design considerations arepresented wherein systems may be capable of accommodating, or potentially even benefitingfrom, fluid/surface fouling. Suggestions for a shift in the method of testing and evaluatingspacecraft management system prototypes are offered to better bound expected operationalconditions, providing more realistic performance data. Two examples of sustainable spacecraftfluid management systems that incorporate these design considerations are presented hereinas case studies. One system is conceived for short duration microgravity flight, and the otherfor long duration planetary use. They are unified by accommodating fluid fouling, rather thanpreventing it, to achieve more sustainable and robust performance.Spacecraft Fluid ManagementIn a microgravity environment, separation of immiscible fluids (i.e. gas and liquid) does notoccur naturally, as it does on Earth due to buoyancy. In such situations, surface tension andwetting forces become the dominant influence on the liquid behavior. The Space Shuttle andthe International Space Station (ISS) both use rotary fans for water separation from anairstream, which are known to be susceptible to failure due to fouling, since the tighttolerances and small orifices do not readily accommodate the resultant blockage that can occurfrom biological or inorganic mass buildup. This potential for clogging adds another concern inaddition to the already generally increased likelihood of failure due to moving parts needed forrotating equipment (Johnson 2002; Puttkamer 2008).Capillary action is regularly used for the control of liquids in various spacecraft systems, such aspropellant and cryogen management or in thermal fluid loops for temperature control(Weislogel, Thomas et al. 2009). Large length-scale capillary systems such as these tend toexploit container geometry and fluid properties to passively transport fluids to desired positionsfor a variety of purposes. Unfortunately, such methods have only been confidently establishedfor well characterized systems with favorable wetting conditions.In contrast to state-of-the-art mechanical approaches, it is anticipated that passive capillarydriven liquid phase separation is feasible in place of active rotary separators for wastewaterapplications, where the wetting and fouling characteristics can vary widely. In a recent study, apassive capillary-driven `static phase separator' was developed and tested in a reduced-gravityenvironment to demonstrate successful air/liquid separation under highly variable wettingconditions (Weislogel, Thomas et al. 2008). When the system was operated within designspecifications, it achieved 100% separation in nearly 100% of the tests performed, and withfluids of widely varying contact angles.In general, geometry-based design considerations based on this principle can be used toimprove the operational reliability of capillary-based microgravity fluid management systems. Adesign strategy begins to emerge when complemented by the following additionalconsiderations.Fluid TreatmentsIn a related study, Thomas and Muirhead (2009) observed that certain aspects of wastewaterfouling can improve wetting characteristics. They found that although vacuum drying and largedefects tended to increase Bad,,, crystal growth and biofilm growth actually lowered Bad,,. Theyalso noted that the use of pretreatments generally increased 6pd,,. These trends indicate thatpromotion of wastewater fouling may be exploited to significantly decrease God„ and therebyimprove performance of capillary-based fluid management systems.The use of oxidizing pretreatment chemicals for spacecraft wastewater is intended to preventurea hydrolysis and the subsequent biofilm and precipitate formation that tends to foul andclog hardware such as rotary fan separators, vacuum orifice, or water recovery systems. Incontrast, the absence of pretreatment chemicals likely results in an increased prevalence ofbiofilm formation and small crystalline growth, which has been shown to significantly lower thecontact angle by up to 44° with 95% confidence (Thomas and Muirhead 2009). This responsecan be utilized by design to increase the performance of a capillary-based wastewatermanagement system. Consequently, an alternate design strategy coinciding with the use of acapillary-based system might be to eliminate the need for pretreatment chemicals intended toprevent fouling, and deliberately allow wastewater fouling to occur in the liquid managementsystem.Lunar Outpost Water RecoveryAs missions become extended in duration and move toward more self-reliant operations, newdemands are placed on the life support system design. Thus far, all indications have suggestedthat the lunar outpost water recovery systems will be evolved from current spacecrafttechnologies, including urine pretreatment, distillation, and brine dewatering (NASA 2005).However, these technologies were developed for microgravity compatibility, and may carryundesirable fouling and failure mode heritage from this environment.Unlike orbiting spacecraft, a lunar outpost will exist in a fractional Earth gravity environment(-0.166go ) with abundant natural resources including lunar regolith, vast open surfaces, andplentiful sunlight. Gravity can at the very least make complex microgravity compatibletechnologies unnecessary, and at best be advantageously utilized in a wastewater recoveryprocess. Meanwhile, the outpost may not have ready access to Earth resupply, makingconsumables and maintenance of greater concern when conducting design trade studies. Lunarsurface conditions are perhaps more analogous to the terrestrial environment than tomicrogravity space flight. For these reasons, the appropriate technology development approachfor lunar outpost hardware may likely be adapting terrestrial technologies for use in a hypo-gravity environment, rather than modifying microgravity space flight technologies.As part of a wastewater management system for a planetary base, an alternative filteringmethod is suggested. The aforementioned fouling studies indicated that wastewater can beexpected to form biofilms, amorphous crystalline deposits, and large crystals on solid surfaces.These constituents are similar to those found in terrestrial water treatment systems, and caneasily be filtered out. For example, wastewater in a lunar outpost could be encouraged to foul,and then these fouling constituents could then be removed by filtering. Potentially, lunarregolith could be used as a media filter. Filtered wastewater is then delivered to the primarydownstream processors. By precipitating crystalline constituents, it is feasible to expect ahigher recovery rate and lower energy cost for the primary processors, which are limited by thesolubility of the ionic concentrations.A primary NASA Exploration Life Support technology activity is "reducing life supportconsumables and improving system performance and robustness," (Barta and Ewert 2009). Thissustainable water recovery concept addresses this gap through the innovative use of partialgravity, solar energy and lunar regolith in place of pretreatment chemicals and primaryprocessors (Thomas, Leidich et al. 2009).High Fidelity Environmental Technology TestingIn addition to the technical design considerations, it is possible that more sustainable spacecraftfluid management technologies might also be developed by reconsidering the methods inwhich they are typically tested under highly controlled conditions. The goal is generally toconduct defined tests that produce predictable and reproducible results akin to how basicscientific research is carried out. Once these systems are in space, however, they often fail incomplex, unforeseen ways leaving the engineers frustrated and the systems in disuse.Designing, testing and evaluating spacecraft fluid management systems is an engineeringchallenge more than it is a basic science research challenge. Rather than examiningfundamental processes, engineers are generally more interested in how well a given systemmeets operational requirements. Testing protocols, therefore, should be adjusted to reflect thisgoal. Systems should not need to be fully characterized under precise and controlledenvironments; rather results from complex and compounded conditions within definedboundaries should be compared to stated performance requirements.While this approach may seem like standard engineering practice, it is in fact a departure fromthe methods in which most spacecraft fluid management systems are tested, perhaps aconsequence of the rarity and expense of 'in-space' field testing. Specifically, the typicalapproach today is to control the testing environment in such a way that any particularrequirement is evaluated in relative isolation. For example, ground tests with fluid systemsoften use ersatz with over-simplified conditions that do not fully represent the actualenvironment that produces the appropriate complex surface conditions in which the foulingoccurs. Engineering performance tests consequently should be less concerned with fullycharacterizing a single parameter in favor of gaining confidence in the system's overallrobustness and sustainability across a range of expected conditions. In this manner, theresultant designs will necessarily be capable of accommodating, if not exploiting, fluid fouling,making the next generation of spacecraft life support and fluid handling systems more robustand sustainable.ConclusionRather than attempting to prevent or reduce fouling, which can result in wastewater systemfailures, sustainable fluid management concepts can be designed to accommodate, perhapseven benefit from, biofouling and mineral scaling. Design considerations including geometryguidelines for capillary-based fluid separators capable of handling highly variable wettingconditions, discontinued need for pretreatment chemicals, and wastewater fouling filtrationoffer feasible approaches.Additionally, rather than evaluating technologies within narrowly controlled experimentalconditions that might not accurately reflect actual complex operational environments, waterhandling systems can be operationally verified over a reasonable envelope of expectedconditions to better ensure their reliability. These considerations can be applied to myriadterrestrial and spacecraft sustainable fluid management technologies.Collectively, the design considerations and application examples presented here are unified bythe approach of accommodating fluid fouling to achieve more sustainable and robust systems.ReferencesBarta, D. and M. Ewert (2009). 2009-01-2483 Development of Life Support System Technologiesfor Human Lunar Missions. International Conference on Environmental Systems. Savannah,SAE.Johnson, J. (2002). EECOM/DF82/JSC-19935 Shuttle OPS V08-Waste Collection System.Houston, NASA-Johnson Space Center.NASA (2005). NASA-TM-2005-214062 NASA's Exploration Systems Architecture Study, NationalAeronautics and Space Administration.Puttkamer, J. (2008). "ISS On-Orbit Status 05/21/08." International Space Station Daily ReportRetrieved November 24, 2008, 2008, fromhttp://www.hq.nasa.gov/osf/iss reports/reports2008/05-21-2008.htm.Thomas, E., J. Leidich and D. Klaus (2009). 2009-01-2503 A Sustainable Regolith-Based WaterRecovery Concept for the Lunar Outpost. International Conference on EnvironmentalSystems. Savannah, SAE.Thomas, E. and D. Muirhead (2009). "Wastewater Fouling Impact on Capillary Contact Angle."Biofouling 2(5): 445-454.Weislogel, M., E. Thomas and J. Graf (2009). "A Novel Device Addressing Design Challenges forPassive Fluid Phase Separations Aboard Spacecraft." Microgravity Science and Technology21(3): 257-268.

Developing Sustainable Spacecraft Water Management Systems

NASA Technical Reports Server

2009-2010 Decadal Survey on Biological and Physical Sciences in Space
National Research Council of The National Academies
Translation to Space Exploration Systems
White Paper Submission
Developing Sustainable Spacecraft Water Management Systems
Evan A. Thomas
NASA- Johnson Space Center
David M. Klaus
University of Colorado at Boulder
Abstract
It is well recognized that water handling systems used in a spacecraft are prone to failure
caused by biofouling and mineral scaling, which can clog mechanical systems and degrade the
performance of capillary-based technologies. Long duration spaceflight applications, such as
extended stays at a Lunar Outpost or during a Mars transit mission, will increasingly benefit
from hardware that is generally more robust and operationally sustainable overtime.
This paper presents potential design and testing considerations for improving the reliability of
water handling technologies for exploration spacecraft. Our application of interest is to devise a
spacecraft wastewater management system wherein fouling can be accommodated by design
attributes of the management hardware, rather than implementing some means of preventing
its occurrence.
Introduction
Development of spacecraft life support hardware over the past few decades has focused
primarily on microgravity applications, with sophisticated designs usually constrained by
limitations of volume, mass and power. In particular, for 2-phase gas/liquid separation in
microgravity, centripetal acceleration or capillary action is used to remove liquids without the
aid of gravity-driven buoyancy. These systems have often been prone to failure due to fluid
fouling caused by biological reactions or mineral scaling, which can clog mechanical systems
and degrade the performance of capillary-based systems. In turn, these failures can cause
increased maintenance cost and overall crew labor burden.
Long duration space missions, such as expected for a Lunar Outpost or a Mars transit, will drive
the need for hardware that is less prone to fouling failure and generally more robust and
sustainable. One application that would benefit from innovation is wastewater management,
wherein wastewater fouling can be accommodated by the design of the fluid management
hardware as opposed to its occurrence being detrimental to the desired process.
https://ntrs.nasa.gov/search.jsp?R=20090039037 2019-08-30T08:14:36+00:00Z
This paper presents challenges associated with spacecraft water system fouling and suggests
alternative approaches that move toward increased sustainability. Design considerations are
presented wherein systems may be capable of accommodating, or potentially even benefiting
from, fluid/surface fouling. Suggestions for a shift in the method of testing and evaluating
spacecraft management system prototypes are offered to better bound expected operational
conditions, providing more realistic performance data. Two examples of sustainable spacecraft
fluid management systems that incorporate these design considerations are presented herein
as case studies. One system is conceived for short duration microgravity flight, and the other
for long duration planetary use. They are unified by accommodating fluid fouling, rather than
preventing it, to achieve more sustainable and robust performance.
Spacecraft Fluid Management
In a microgravity environment, separation of immiscible fluids (i.e. gas and liquid) does not
occur naturally, as it does on Earth due to buoyancy. In such situations, surface tension and
wetting forces become the dominant influence on the liquid behavior. The Space Shuttle and
the International Space Station (ISS) both use rotary fans for water separation from an
airstream, which are known to be susceptible to failure due to fouling, since the tight
tolerances and small orifices do not readily accommodate the resultant blockage that can occur
from biological or inorganic mass buildup. This potential for clogging adds another concern in
addition to the already generally increased likelihood of failure due to moving parts needed for
rotating equipment (Johnson 2002; Puttkamer 2008).
Capillary action is regularly used for the control of liquids in various spacecraft systems, such as
propellant and cryogen management or in thermal fluid loops for temperature control
(Weislogel, Thomas et al. 2009). Large length-scale capillary systems such as these tend to
exploit container geometry and fluid properties to passively transport fluids to desired positions
for a variety of purposes. Unfortunately, such methods have only been confidently established
for well characterized systems with favorable wetting conditions.
In contrast to state-of-the-art mechanical approaches, it is anticipated that passive capillary
driven liquid phase separation is feasible in place of active rotary separators for wastewater
applications, where the wetting and fouling characteristics can vary widely. In a recent study, a
passive capillary-driven `static phase separator' was developed and tested in a reduced-gravity
environment to demonstrate successful air/liquid separation under highly variable wetting
conditions (Weislogel, Thomas et al. 2008). When the system was operated within design
specifications, it achieved 100% separation in nearly 100% of the tests performed, and with
fluids of widely varying contact angles.
In general, geometry-based design considerations based on this principle can be used to
improve the operational reliability of capillary-based microgravity fluid management systems. A
design strategy begins to emerge when complemented by the following additional
considerations.
Fluid Treatments
In a related study, Thomas and Muirhead (2009) observed that certain aspects of wastewater
fouling can improve wetting characteristics. They found that although vacuum drying and large
defects tended to increase Bad,,, crystal growth and biofilm growth actually lowered Bad,,. They
also noted that the use of pretreatments generally increased 6pd,,. These trends indicate that
promotion of wastewater fouling may be exploited to significantly decrease God„ and thereby
improve performance of capillary-based fluid management systems.
The use of oxidizing pretreatment chemicals for spacecraft wastewater is intended to prevent
urea hydrolysis and the subsequent biofilm and precipitate formation that tends to foul and
clog hardware such as rotary fan separators, vacuum orifice, or water recovery systems. In
contrast, the absence of pretreatment chemicals likely results in an increased prevalence of
biofilm formation and small crystalline growth, which has been shown to significantly lower the
contact angle by up to 44° with 95% confidence (Thomas and Muirhead 2009). This response
can be utilized by design to increase the performance of a capillary-based wastewater
management system. Consequently, an alternate design strategy coinciding with the use of a
capillary-based system might be to eliminate the need for pretreatment chemicals intended to
prevent fouling, and deliberately allow wastewater fouling to occur in the liquid management
system.
Lunar Outpost Water Recovery
As missions become extended in duration and move toward more self-reliant operations, new
demands are placed on the life support system design. Thus far, all indications have suggested
that the lunar outpost water recovery systems will be evolved from current spacecraft
technologies, including urine pretreatment, distillation, and brine dewatering (NASA 2005).
However, these technologies were developed for microgravity compatibility, and may carry
undesirable fouling and failure mode heritage from this environment.
Unlike orbiting spacecraft, a lunar outpost will exist in a fractional Earth gravity environment
(-0.166go ) with abundant natural resources including lunar regolith, vast open surfaces, and
plentiful sunlight. Gravity can at the very least make complex microgravity compatible
technologies unnecessary, and at best be advantageously utilized in a wastewater recovery
process. Meanwhile, the outpost may not have ready access to Earth resupply, making
consumables and maintenance of greater concern when conducting design trade studies. Lunar
surface conditions are perhaps more analogous to the terrestrial environment than to
microgravity space flight. For these reasons, the appropriate technology development approach
for lunar outpost hardware may likely be adapting terrestrial technologies for use in a hypo-
gravity environment, rather than modifying microgravity space flight technologies.
As part of a wastewater management system for a planetary base, an alternative filtering
method is suggested. The aforementioned fouling studies indicated that wastewater can be
expected to form biofilms, amorphous crystalline deposits, and large crystals on solid surfaces.
These constituents are similar to those found in terrestrial water treatment systems, and can
easily be filtered out. For example, wastewater in a lunar outpost could be encouraged to foul,
and then these fouling constituents could then be removed by filtering. Potentially, lunar
regolith could be used as a media filter. Filtered wastewater is then delivered to the primary
downstream processors. By precipitating crystalline constituents, it is feasible to expect a
higher recovery rate and lower energy cost for the primary processors, which are limited by the
solubility of the ionic concentrations.
A primary NASA Exploration Life Support technology activity is "reducing life support
consumables and improving system performance and robustness," (Barta and Ewert 2009). This
sustainable water recovery concept addresses this gap through the innovative use of partial
gravity, solar energy and lunar regolith in place of pretreatment chemicals and primary
processors (Thomas, Leidich et al. 2009).
High Fidelity Environmental Technology Testing
In addition to the technical design considerations, it is possible that more sustainable spacecraft
fluid management technologies might also be developed by reconsidering the methods in
which they are typically tested under highly controlled conditions. The goal is generally to
conduct defined tests that produce predictable and reproducible results akin to how basic
scientific research is carried out. Once these systems are in space, however, they often fail in
complex, unforeseen ways leaving the engineers frustrated and the systems in disuse.
Designing, testing and evaluating spacecraft fluid management systems is an engineering
challenge more than it is a basic science research challenge. Rather than examining
fundamental processes, engineers are generally more interested in how well a given system
meets operational requirements. Testing protocols, therefore, should be adjusted to reflect this
goal. Systems should not need to be fully characterized under precise and controlled
environments; rather results from complex and compounded conditions within defined
boundaries should be compared to stated performance requirements.
While this approach may seem like standard engineering practice, it is in fact a departure from
the methods in which most spacecraft fluid management systems are tested, perhaps a
consequence of the rarity and expense of 'in-space' field testing. Specifically, the typical
approach today is to control the testing environment in such a way that any particular
requirement is evaluated in relative isolation. For example, ground tests with fluid systems
often use ersatz with over-simplified conditions that do not fully represent the actual
environment that produces the appropriate complex surface conditions in which the fouling
occurs. Engineering performance tests consequently should be less concerned with fully
characterizing a single parameter in favor of gaining confidence in the system's overall
robustness and sustainability across a range of expected conditions. In this manner, the
resultant designs will necessarily be capable of accommodating, if not exploiting, fluid fouling,
making the next generation of spacecraft life support and fluid handling systems more robust
and sustainable.
Conclusion
Rather than attempting to prevent or reduce fouling, which can result in wastewater system
failures, sustainable fluid management concepts can be designed to accommodate, perhaps
even benefit from, biofouling and mineral scaling. Design considerations including geometry
guidelines for capillary-based fluid separators capable of handling highly variable wetting
conditions, discontinued need for pretreatment chemicals, and wastewater fouling filtration
offer feasible approaches.
Additionally, rather than evaluating technologies within narrowly controlled experimental
conditions that might not accurately reflect actual complex operational environments, water
handling systems can be operationally verified over a reasonable envelope of expected
conditions to better ensure their reliability. These considerations can be applied to myriad
terrestrial and spacecraft sustainable fluid management technologies.
Collectively, the design considerations and application examples presented here are unified by
the approach of accommodating fluid fouling to achieve more sustainable and robust systems.
References
Barta, D. and M. Ewert (2009). 2009-01-2483 Development of Life Support System Technologies
for Human Lunar Missions. International Conference on Environmental Systems. Savannah,
SAE.
Johnson, J. (2002). EECOM/DF82/JSC-19935 Shuttle OPS V08-Waste Collection System.
Houston, NASA-Johnson Space Center.
NASA (2005). NASA-TM-2005-214062 NASA's Exploration Systems Architecture Study, National
Aeronautics and Space Administration.
Puttkamer, J. (2008). "ISS On-Orbit Status 05/21/08." International Space Station Daily Report
Retrieved November 24, 2008, 2008, from
http://www.hq.nasa.gov/osf/iss reports/reports2008/05-21-2008.htm.
Thomas, E., J. Leidich and D. Klaus (2009). 2009-01-2503 A Sustainable Regolith-Based Water
Recovery Concept for the Lunar Outpost. International Conference on Environmental
Systems. Savannah, SAE.
Thomas, E. and D. Muirhead (2009). "Wastewater Fouling Impact on Capillary Contact Angle."
Biofouling 2(5): 445-454.
Weislogel, M., E. Thomas and J. Graf (2009). "A Novel Device Addressing Design Challenges for
Passive Fluid Phase Separations Aboard Spacecraft." Microgravity Science and Technology
21(3): 257-268.


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